<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>太极图</title>

    <style>
        .tj{
            width: 100px;
            height: 50px;
            border: 1px solid black;
            border-bottom: 50px solid black;

            /*画个正圆*/
            border-radius: 50%;

            position: relative;
        }

        .tj:before{
            width: 10px;
            height: 10px;
            border: 20px solid black;
            content: " ";
            border-radius: 50%;
            background: white;

            position: absolute;
            top: 25px;
            left: 0px;
        }

        .tj:after{
            content: ' ';
            width: 10px;
            height: 10px;
            border: 20px solid white;
            background: black;
            border-radius: 50%;
            position: absolute;
            top: 25px;
            right: 0px;
        }


    </style>

</head>
<body>


<div class="tj"></div>

</body>
</html>